As I mentioned in a previous topic, the usage of the simple cables between the handheld transceiver and Android device is not always a 100% reliable solution, mainly because some Android devices can not be configured to "accept" audio signals on their MIC input or, if accept, they have an unwanted behavior (e.g. start the music player).
For this reason, and taking the advantage of the bluetooth option provided by APRSdroid software, I decided to try to transform a bluetooth headset in a small interface between Android phone and the VHF transceiver. I choose a cheap earpiece (around 7 EUR) available on local market (LAZER Auriclar Bluetooth), the only special thing on it being the multipoint feature. This is not mandatory, the only reason being that such a feature are available on a newer bluetooth modules.
Carefully unscrew the earpiece case and identify and unsolder the wires for input (those connected to the microphone) and output (those connected to the speaker. Then, it is important to identify the right ground. Usually, this is the same with the battery's minus and microphone's ground. Use not only an Ohm-meter, but also a visual check of the PCB.
Most of the bluetooth earphones use a so called "H output circuit" (to increase the audio level with low supply voltage) and for this reason any (but only one) of the output wires can be used further, the unused wire following to be isolated.
Because the device wires are too thin, you will need to manage the connections with the transceiver in a new case, through a proper connector/outlet. For this reason, you have to identify, also, how the device can be recharged in a different way than the original connector.
But, before trying to fit the bluetooth PCB and the battery in a proper case, test it with APRSdroid, following the below schematic:
On APRSdroid side, first, be sure that you have installed at least version 1.2.2, because starting with this version was implemented the bluetooth support for AFSK signal. Check the latest vesrion at the official APRSdroid site.
Enable bluetooth on your Android device, then start the bluetooth headset, put it in visiblity mode and complete the pairing and interconnectivity between devices. When this step is done, start APRSdroid and continue with the configuration:
in "Connection Preferences" section, select "Connection Protocol", then Audio (AFSK) option;
this will change the preferences menu with different options:
check High-Quality Demodulator option;
check Bluetooth Headset;
set Audio Output on Voice Call;
set Frame Sync Prefix between 200 and 300 msec;
set APRS digipath as WIDE1-1 at this moment, for tests.
Go to the main interface of the APRSdroid application and push . For transmitting APRS packets, will be necessary to increasethe phone's audio level over 70%.
If all works OK, try to find a proper case. Personally, I used a small remote case, for cars remote controls, that I set an on / off button and two outlets, a mono one for charging and a stereo one for audio in/out to the phone.
